1. Field of the Invention
The present invention relates to tennis racquets, and more particularly, to tennis racquets of greater than conventional length.
2. Prior Art
Many theories of design of tennis racquets have been developed in an attempt to enhance the playing characteristics of a racquet so that it is easier to swing, causes less shock to the arm of the player and provides sufficient strung surface area to present a reasonable size hitting surface for the ball. There is a particularly popular theory at present relating to the positioning of the center of percussion or the so called "sweet spot" of the strung surface area of the racquet, as close as possible to the center of the strung surface are of the racquet to develop certain alleged advantages of the location in this manner such as reduced jar to the players hand and arm. A detailed discussion of such advantages and one manner of relocating the center of precussion closer to the center of the strung area from that of conventional or standard tennis racquets are disclosed in Head U.S. Pat. No. 3,999,756.
However, an analysis of the practical aspects of actual use of a tennis racquet indicates that the positioning of the sweet spot, whether it be approximately 1/3 the distance from the yoke to the center of the strung surface as is the case in most conventional racquets or whether it is moved to a position half the distance from the yoke to the center of the strung surface area as is the case in the racquet proposed in the above identified patent, is of little consequence from the actual point of view as the racquet is used in play.
In analysis of the position of the center of percussion it is generally assumed that the racquet pivots about a line approximately 3 inches from the butt end of the handle of the racquet which corresponds to the position of the wrist of the player. The analysis can be analogized to a pendulum-like rod pivotally mounted at one end and free to swing about the pivot point so that the center of precussion will be at a distance from the pivot point such that no reaction force will be felt at the pivot point in response to application of a force at the center of precussion.
The fallacy in such analysis is that in practical application, the pivotal connection, i.e. the wrist of the player, and the flexibility or rigidity thereof are totally dependent upon the strength of the grip of the player, which varies greatly. Also, in most playing strokes the wrist is actually held rigid, and the racquet and arm of the player, as well as the torso, are rotated thus actually providing a much larger radius of rotation than would be the case if the racquet were merely swung from the wrist.
Further, in many other shots the racquet, wrist and arm are held rigid along with the torso of the player as the player moves forward into the ball so that motion of the racquet during the period of contact with the ball is substantially translational rather than rotational, which even further distorts the value of determining the center of precussion of the racquet. This is so because in purely translational motion, i.e. pivoting at infinity, the center of percussion is located at the center of gravity which is somewhere on the handle of most racquets, while for rotational motion, the center of percussion for tennis racquets is outward from the center of gravity, usually on the strung surface adjacent the yoke or approaching the center of the strung surface.
Therefore the significance of repositioning the center of percussion from approximately 1/3 the distance from the yoke to the center of the strung surface of the racquet to a position closer to the center of the strung surface is much reduced under actual playing conditions and does little to enhance the playing characteristics of the racquet.
On the other hand, what is of significance is the polar moment of inertia of the racquet about the axis through which the racquet can reasonably be considered as actually rotating under practical playing conditions. Since most shots of a rotational nature are performed by maintaining a rigid wrist and arm and rotating the torso of the player during the period of contact of the ball, it is presumed that such an axis would be located at approximately the spine of the player, which can be presumed to be approximately two feet from the butt end of the racquet.
The polar moment of inertia is essentially the resistance to acceleration which a racquet exhibits as it is being swung. Many players who have used a plurality of different types of racquets have experienced a significant difference in the way each racquet plays. The majority of this difference, so far as the "feel" of the racquet is concerned, is associated with the polar moment of inertia of the racquet. Some racquets feel "heavy" or sluggish when they are swung. This is due to the greater polar moment of inertia of such racquets compared to other racquets which feel "light" or are more easily swung. Thus, the polar moment of inertia of the tennis racquet is clearly a very important consideration in the value of a tennis racquet, and one which has not heretofore been given sufficient recognition.
As most tennis players know, and as pointed out in Dean U.S. Pat. No. 3,833,219, the conventional, standard tennis racquet has dimensions which in part are derived from the prescribed 36-inch height of the tennis court net at its center. The total longitudinal measurement of a conventional wood racquet is therefore 27 inches while the transverse dimension of the oval racquet head measured at the minor axis thereof is 9 inches, which when added to the longitudinal dimension of the racquet gives the 36-inch dimension.
The corresponding inside dimension or width of the conventional oval racquet head will of course depend upon the thickness of the frame, but according to Mason U.S. Pat. No. 3,515,386, this dimension is approximately 81/4 inches for a conventional racquet. Also according to the Mason patent, the maximum longitudinal dimension of the strung surface of a conventional racquet is approximately 103/4 inches, to which of course must be added the thickness of the frame portions at opposite ends of the head. Mason also states that the conventional tennis racquet has a handle which is 147/8 inches in length, which would mean that the overall length of the head portion of a conventional racquet is 121/8 inches to provide the conventional overall length of 27 inches.
The only substantial departure from these general dimensional limitations which has made any significant impact in the tennis playing community is the "Prince" racquet of the above noted Head U.S. Pat. No. 3,999,756. According to that patent, its racquet may have an overall length of between 26 and 28 inches, but the preferred embodiment has the conventional overall length of 27 inches. The head portion, however, is substantially larger than a conventional racquet, the preferred embodiment defining a strung area about 131/2 inches long and about 101/2 inches wide, or about 60% larger than the average corresponding area of a conventional racquet. Head, however, emphasizes that its racquet is of standard length, weight, and balance.
In approaching the description of the present invention, therefore, it can be assumed that conventional racquets are generally 27 inches in length although the length appears to vary between 26 and 28 inches for some of the more unusual designs. The advantages of a longer racquet are obvious in that it increases the "reach" of a player, thus reducing the amount of movement required by the player across the court in order to hit the ball. One factor which has restricted the length of a racquet is that longer racquets appear to be top heavy, and too much weight is placed in the head since such racquets are generally just a scaled up version of the standard racquet length and size and are thus generally undesirable and have not met with success.
The usefulness of an increased strung surface area over standard or conventional racquets is shown by the success of the racquets made in accordance with the above Head patent. However, the teachings of the prior art are such that no one heretofore has attempted to lengthen the racquet as well as to increase the size of the strung area, because of the awkwardness of the feel of the racquet as it would no doubt be made in accordance with such teachings.